Keep your dog in the back. Driving with her in the front is unsafe—and illegal in some places.

Coordinate rest stops. Each time you pull over for a bathroom or water break, be sure to extend the same courtesy to your dog.

Consider your pet's comfort. If it's hot, park in the shade and leave water out and the AC running—cars can warm up rapidly in hot temperatures, resulting in fatal heatstroke. Likewise, in extremely cold temps, keep the heater turned up to prevent your pooch from freezing.

In a minivan, SUV, or station wagon: A crate is a smart choice, says Christie Hyde, automotive/driver safety spokesperson for AAA National. Even a divider between the backseat and trunk/cargo area isn't enough to protect your pet in a crash. Make sure the crate is large enough for her to stand, sit, lie down, and turn around--but not so large that she can pace. Place the crate in the back, facing forward (to prevent car sickness). Pick a hard crate for safety and unclip her leash to prevent dangerous tangling.

In a sedan or sporty two-door model: A crate might not fit in the backseat. A seatbelt harness, available at pet stores for about $20, will keep her secure. Look for one with a broad front, lots of padding, sturdy metal hardware, and wide straps that are made of a seatbeltlike material.

Carry on your small breed. Some airlines will allow you to take little dogs or cats on board in a soft-sided carrier. The fee is usually $100 each way, and your pet must stay in the carrier under the seat at all times.